Mechanisms, controlled responsively to the occurrence of a slipping condition of a vehicle wheel due to excessive application of an air-operated brake, for effecting a reduction in the degree of the brake application and a subsequent increase in the degree of the brake application in a manner to prevent the sliding of the vehicle wheels have been used for many years in both the railway and automotive industries.
In recent years hydro-pneumatic brake units have been successfully used experimentally to apply a braking force to each individual wheel of rapid transit vehicles. It is, therefore, apparent that apparatus, controlled responsively to the occurrence of a slipping condition of the individual wheel due to the application of excessive braking force thereto, for effecting a reduction in the degree of this braking force and a subsequent increase in the retarding force applied to the wheel in such a manner as to prevent sliding of the wheel would be most desirable.
Accordingly, it is the general purpose of this invention to provide a brake control apparatus for a hydro-pneumatic brake unit that includes a power-actuated brake-applying-force relief valve device which is automatically operative responsive to the occurrence of a slipping condition of a vehicle wheel to cause a reduction in the degree of the hydraulic brake application effected by the brake unit and a subsequent increase in the brake application upon cessation of the slipping condition.